In a camera, when a flash is activated or when the film is wound up or rewound, the battery voltage drops markedly. Therefore, it is impossible to use the battery for driving the camera directly as a power supply for displaying a date on a liquid crystal display unit, for example. Accordingly, in the prior art camera, as shown in FIG. 5, a separate power supply battery 53 is provided for activating a display unit driving circuit 52, in addition to the camera driving power supply 51. Alternatively, as shown in FIG. 6, a capacitor 61 of large capacitance is connected across the battery power source for the display unit driving circuit 52, in order that the display unit driving circuit 52 is not subjected to the harmful influence of a drop in the battery voltage caused when the camera is operated under a large load.
In the prior art methods, however, since the separate battery for the display unit driving circuit, or the capacitor, is large in size, a large space is inevitably required. In particular when an to connect the battery and the display unit driving circuit, a considerable space is needed. In addition, there exists the problem that the cost of the camera is increased.